The present invention relates to an electronic digital thermometer for measuring temperature on the basis of the temperature dependence of the resistance value of a temperature-sensitive resistive element. More particularly, the invention relates to a digital thermometer for detecting temperature such as bodily temperature on the basis of an oscillating frequency change, due to temperature change, of an oscillator to which a temperature-sensitive resistive element is connected as a frequency determining element.
A typical prior art electronic thermometer comprises a pulse oscillator to which a temperature-sensitive resistor such as a thermistor is connected as a oscillation frequency determining element, a temperature output circuit including a counter connected to the pulse oscillator, a digital display device connected to the counter and a time decision circuit for applying the output pulses of the pulse oscillator to the counter during a predetermined time interval. The time decision circuit is arranged so as to supply pulses during one second of time interval to the counter. Accordingly, the counter counts the temperature-dependent oscillating frequency of the pulse oscillator and the digital display device displays a measured temperature value corresponding to the oscillating frequency. In this prior art, temperature is directly measured by the temperature-dependent oscillating frequency, and thus parts (passive elements) which have high accuracy and are little subject to ageing are required. In addition, with the prior art, it is difficult to correctly measure temperature due to possible variation in the oscillating frequency resulting from the variations in the power supply voltage and operating conditions of active elements used.